This invention relates generally to electric lamps utilizing one or more resistive incandescent filaments as the illumination source and wherein said illumination source is physically connected to at least one pair of conductive inlead wires of dispersion strengthened copper alloy serving as the sole means of physical support for said illumination source. Electric lamps of this type are described in U.S. Pat. No. 4,208,603, assigned to the assignee of the present invention, with said inlead construction exhibiting improved stiffness sufficient to eliminate the need for additional support of the incandescent filament by the previously employed tie wire elements. An incandescent electric lamp having said improved inlead construction includes a transparent envelope with a stem press seal region at one end containing the said resistive incandescent filament phsyically connected to a pair of conductive inlead wires of dispersion strengthened copper alloy providing said physical support and with said inlead wires extending through said stem press seal region. In a different incandescent lamp construction, the transparent envelope contains a pair of resistive incandescent filaments and two pair of conductive inlead wires of dispersion strengthened copper alloys serving as the sole support for each incandescent filament, and with one inlead wire of each pair of inlead wires being connected together in common for lamp operation at different levels of illumination. A third type electric lamp is also described in said prior art patent utilizing an outer transparent envelope which contains at least one resistive incandescent filament and an inner sealed arc tube as separate illumination sources and with said incandescent illumination sources being connected to a pair of conductive inlead wires of dispersion strengthened copper alloy serving again as the sole means of physical support for said illumination sources.
It has longer been known to provide fuse leads in various type electric lamps to avoid the arc damage caused if abnormally high electrical currents are applied to the lamp. Said fuse leads generally operate toward the end of lamp life, when the filament fails during lamp operation and commonly forms an arc, thereby resulting in increased current flow which causes the fuse lead wire to be blown or ruptured. The rupturing of the fuse often causes spattering of molten metal and metallic vapor throughout the stem press region of the lamp envelope with resultant violent arcing and likelihood of damage to the lamp and to the socket in which the lamp is mounted. A commonly employed form of such fuse lead is a wire of nickel or copper-silicon alloy physically joined to one of the lamp inleads in the stem press region of the lamp envelope.
Excessive lamp arc damage is still being experienced with conventional fuse leads due to spattering of the molten metal inside the lamp envelope. While protective sleeves have also been employed over the fuse leads to ameliorate this problem, the attendant cost and effort in adding such further protective means is understandably not very satisfactory. Fuse metals also melt at various rates dependent upon the lamp current and with faster melting action minimizing arc damage in the lamp. It would be advantageous, therefore, to provide improved fuse leads demonstrating faster melting rates especially at higher current levels and which do not spatter excessively when melted.